(1) Field of the Invention
The invention relates to processing of digital images, and more particularly to writing digital line based pixel data into a buffer memory comprising block based pixel data and relates to reading out these pixel data for further processing.
(2) Description of the Prior Art
Usually the output of imagers as e.g. digital cameras or scanners is pixel line oriented. Applications as e.g. mirroring of images or image compression require a block of pixel data. A buffer memory is commonly used to store the pixel data prior to further processing.
FIG. 1 shows a typical data flow of such a pixel line to pixel block conversion. An imager 1 as e.g. a digital camera provides line based pixel data, the next block 2 provides a conversion from line based pixel data to block based pixel data stored in a buffer memory to be read out for further processing as required by an following application 3, as e.g. mirroring of an image or image compression. Such image applications require a block of pixel data. A buffer memory is required to store said block of pixel data for further processing.
FIG. 2 a to FIG. 2 d prior art show how consecutively line based pixel data are filled into this buffer memory and read out by a related application. In FIG. 2a prior art the buffer memory 20, comprising an upper half 21 and a lower half 22 is empty. Both upper 21 and lower 22 halves have a capacity to store one complete image each. In FIG. 2b prior art the upper half 21 of the buffer memory 20 is filled line by line with pixel data from an imager until all pixels of a fist image are stored in the upper half 21 while the lower half 22 is still empty. In FIG. 2c prior art the pixels the image stored in the upper half 21 of the buffer memory 20 are read out while at the same time the lower half 22 is filled with pixel data of a second image, and in FIG. 2d prior art the upper half 21 is filled again with pixel data of a third image while the pixels of the second image stored in the lower half 22 are read out. This process of filling one half of the buffer memory 20, reading out the other half of the buffer memory 20 and vice versa is then continued until the end of the process. It is obvious that a buffer memory operated with such a method requires a size big enough to store all pixels of two images. Such a large buffer memory is expensive and requires high power consumption.
There are various patents known in the area of handling pixel data:
U.S. Pat. No. 6,496,222 (to Roberts et al.) describes a digital camera including a digital memory system having a control unit for checking for proper format initialization of a removable digital memory element and for performing format initialization of the memory element when necessary. Upon completion of an image conversion, the contents of a frame buffer are transferred to a compression processor.
U.S. Pat. No. 6,483,540 (to Akasawa et al.) discloses a digital camera comprising a pick-up image data memory for storing pick-up image data by a couple charged device (CCD), a title message table for storing a plurality of title message data to be superimposed over the pick-up image data and a plate table for storing a plurality of plate image data to be overwritten the title message data and a central processing unit (CPU). The CPU overwrites the title message data stored in the title message table on the plate image data stored in the plate table and superimposed the title message data with the plate image data over the pick-up image data stored in the pick-up data memory. Further, the CPU stored the superimposed pick-up image data in the pick-up image memory so that the superimposed image data can be reproduced following the original pick-up image data.
U.S. Pat. No. 6,661,452 (to Nishikawa) discloses a digital camera including an SDRAM. The camera data taken is first written on a camera data area formed in the SDRAM, and thereafter read out 8 lines a time. This 8-lines camera data is YUV-converted by a signal processing circuit. The resulting 8-lines YUV data is stored in a work area of the SDRAM. A JPEG CODEC reads the YUV data block by block out of the work area, and compresses it. The compressed data is written block by block over the camera data area. At this time, the compressed data is written over in a manner avoiding camera data uncompleted of compression. Such a process is repeated very 8 lines. If compressed data is obtained for all of the camera data stored within the camera data area, the compressed data is recorded at one time into a flash memory.